The expansion of gene mapping in man and certain model species for genetic analysis has led to an increased emphasis on using comparative genome organization as a method to deduce gene action in vertebrates. The mouse has served as the primary model for gene mapping in mammals with over 1,000 genes assigned, but the growth of several other domestic species' gene maps in different mammalian orders has been accelerated. We have concentrated on building a gene map of the domestic cat and on developing the cat as a model for genetic analysis in mammals. Interspecies crosses between F. catus and the leopard cat (Prionailurus bengalensis) and between F. catus and Leopardus geoffroyi have been initiated in order to produce backcross offspring to define a linkage map of domestic cat. To date, over 50 interspecies hybrid offspring have been born following artifical insemination; of these, 12 healthy females are maturing. Methods for in situ hybridization of feline metaphase chromosomes using biotin-labeled molecular clones have been attempted and improved. Procedures using human chromosome libraries for chromosome "painting," i.e., visualization of homologous chromosome segments between carnivores and primates, are in progress.